In a multiple head drilling apparatus, the workpiece, such as a wide flange beam, is fed into the machine on guide rollers. Upper and side assemblies each carry spindle blocks on which are mounted the drill heads. The spindle blocks are moved relative to the respective assemblies to position the drill heads at the proper location for drilling holes in both the flanges and web of the beam.
Recently multiple head drilling machines have been programed through electronic controls in which the beam is advanced and the drill heads are actuated through computerized controls.
When dealing with long beams, and particularly beams having a web of substantial depth, the web may not be entirely planar and may have irregularities in the contour. When drilling holes in the web and flanges, it is necessary to accurately establish the position of the web so that the holes can be drilled at the precise location. In situations where the web is not uniformly planar, the irregularities in the web can cause inaccurate locating of the holes to be drilled in the side flanges.